This invention relates to methods of treating surfaces exposed to icing conditions to reduce the bond strength of ice and facilitate its removal from such surfaces.
The accumulation of ice on structures exposed to icing conditions presents problems which may arise from the weight or thickness of the ice. Consequently, it is often necessary to remove ice from ice-coated surfaces. An ice layer may be removed by application of thermal energy to the interfacial bond or by mechanical methods. Thermal methods are slow, require large expenditures of energy, and may be ineffective in some areas, such as the northern portions of the United States where the winter temperatures are extremely low. Mechanical methods involving breaking the ice from structural surfaces are fast and energy-efficient; however, the high strength of adhesion of ice to many surfaces makes ice removal difficult. Furthermore, the strength of adhesion of ice to substrate surfaces such as concrete may exceed the strength of the substrate material and cause the substrate to break or spall.
Icing presents special problems in the lock system for navigating the Great Lakes where ice can build up in layers thick enough to prevent the passage of large vessels. Ice forms on the surfaces of lock walls by direct freezing of water as it comes into contact with the cold wall surface or by the adhesion of floating ice onto a cold wall. This latter process occurs primarily when a ship entering a lock pushes floating ice into the lock area.
The thickness and depth of the ice on the walls depend on factors such as weather, ice conditions outside the lock, traffic, water level, and lock operating procedures. In the Great Lakes area, ice build-up extending four feet into the water channel from the lock walls is not uncommon. This ice reduces the clearance between the walls and the sides of the entering vessels. When the clearance is low, an entering ship can push floating ice into the lock and become wedged while entering.
Since a significant build-up of ice will prevent large ships from passing through the locks, efficient operation of the locks requires that ice be removed. Several methods of removing ice from lock walls have been tested including: (1) use of high pressure (10,000 psi) water jets to cut the ice; (2) attachment of an inflatable boot to the wall which sheds the ice when expanded; (3) use of a saw to cut the ice; and (4) attachment of electrically conductive concrete panels to the lock wall. Ice was removed from the walls using these methods; however, all were time-consuming, and techniques to increase the efficiency of these or other methods have been sought.
One reason for the difficulty in removing ice is the high adhesion strength between the ice and the wall at ambient winter temperature and a reduction in this adhesion by use of a suitable ice release agent would facilitate ice removal.
Ice release agents should not only have low adhesive strength to ice, but also have good film integrity, high abrasion resistance and excellent substrate adhesion. The severe conditions encountered in removing ice from navigation lock surfaces require that the ice release agents be able to resist the forces encountered in removing the large amounts of ice, adhere to the highly porous and soiled concrete surfaces to be treated, and survive the many repetitions of the ice removal during the season. Further, a material is required which can be applied in relatively thick layers and be capable of being applied under adverse conditions, i.e., in the presence of moisture encountered from the seepage, rain, and operation of the lock.